About This File
To be honest I am not sure if there is a higher version of Flat Package Editor, that's the only one I was able to find and it was not working under Mojave.
As far as I can tell it is working, at least I was able to use it for what I needed it.
You might have to open the Terminal and
xattr -r -d com.apple.quarantine <Drag and Drop Flat Package Editor.App> in order to run it